U.S. Geological Survey, in cooperation with Miami-Dade County, performed a sequential, aquifer stress test from August 15 to October 12, 2011, on the Floridan aquifer system at the North District Wastewater Treatment Plant, in Miami-Dade County, Florida. Miami-Dade County stressed the Floridan aquifer system with four municipal injection wells at the North District Wastewater Treatment Plant. Injection wells IW1, IW3, and IW4 stressed the aquifer system with injection of as much as 1.8 cubic meters of effluent per second. Injection well IW2 stressed the aquifer system with pressure release from the injection zone, caused by reverse flow of as much as 0.04 cubic meters of formation fluid mixed with effluent per second, such that pressurized formation fluid from the injection zone flowed up well IW2, into the plant.